/Engine/Source/Runtime/GeometryFramework/Public/Components/DynamicMeshComponent.h
This function is passed via lambda to the RenderProxy when BaseDynamicMeshComponent::ColorMode == Polygroups
[FColor](API\Runtime\Core\Math\FColor) GetGroupColor ( const [FDynamicMesh3](API\Runtime\GeometryCore\DynamicMesh\FDynamicMesh3) * Mesh, int TriangleID ) const